Hi - I'd deeply appreciate a knowledgable opinion or two about the potential validity of the following concept, or how it might be tweaked to correct the science of it, make it more believable to a sci-fi readership -

A group of eighty humans make it to an island after crashing on another planet. They inadvertently infect the native population (a simple, fishing/agrarian culture) w/ human diseases (no immunity), & the few surviving natives give tasty but pathogen-infested eel eggs to the humans, in hopes of killing them off. (The pathogen could be a parasite, or an algae, or... )
They do it this way to get the pathogen into ALL the humans, knowing they'll all eventually die out, without seeing it coming. The natives, though not 'rocket scientists', are very patient, & in the extremity of their situation & limited access to anything else, it's all that comes to mind to do.

The delicious eggs have no ill effect until late in the original partaker’s lifespan, but their children are born fully addicted to it, symptoms showing up at puberty. The withdrawal symptoms are psychologically & physically devastating, & each year this 2nd generation needs more & more to stave off the symptoms.

The microscopic pathogen, making it’s home exclusively within the eggs, developed this deadly addictive quality in order to eliminate any animals that would otherwise eat the eggs. It 'sets out' to addict any egg-predatory animals in order to eliminate that specie's next generation permanently from the environment - like the natives, it also is very patient, and the end result very thorough.
(A mass of gel forms around the eggs in the eel’s body, encapsulating the eggs (& the pathogen) to ’wall it off’ from migrating out & addicting & killing it‘s host.)
The pathogen migrates into the embryonic reproductive system of the young egg-bound eels just before they hatch out, infesting the next generation of eels - this happens within humans as well, but lacking the protective gel, humans are wide open to the spread of the pathogen throughout their bodies.

The humans, eventually, will discover that the addiction’s cure is the active ‘blocking’ factor in the gel, & a quantity of gel must be held in the mouth for, say, fifteen minutes to effectively ’poison’ the pathogen (this pathogen-killing factor is absorbed through the mucous membranes, like sub-lingual B-12, to bypass break-down by the liver).

As you describe it, the second-generation is so desirous of the eggs that they would wipe out that generation of eels / eggs / pathogens.

Why have a pathogen in the eggs at all (as in, why not a toxin)? A toxin is a much more likely defense, and the scenario you're describing would benefit the eels, but not the pathogen.

Add to this the trapped nature of the pathogen in the descending lines of eels, it's unlikely that the eels wouldn't have selective pressure to eliminate the pathogen.

Of course, the whole premise of these pathogens moving back-and-forth between entities whose chemistries evolved on different planets is pretty far-fetched, but kind of a necessary evil of a lot of science fiction.

Kotoreru - the pathogen would always have a safe 'home' in the eggs of the eels. the eels would always have a weapon to completely wipe any potential egg-predatos from the local environment.

Darby - the eels don't want to get rid of the pathogen, they carry it along to destroy anything that might gobble it's eggs. A long-range 'plan'. You're right, though, it would be more logical for some kind of immediate effect to take effect - maybe the pathogen/toxin would have that immediate effect on this planet's creatures, but a DELAYED effect on humans? Sound better?

questions: (1) - could a toxin be addictive like this?
(2) - could a pathogen or toxin utilize germ cells to pass itself into the next generation's DNA w/ a timed manifestation effect like described?